1. Field of the Invention
The present invention relates to an information processing apparatus, an information processing method and a computer readable medium for print control that control a transparency process.
2. Description of the Related Art
Conventionally, an art of alpha blending is known that combines two images by using a coefficient (i.e., alpha value). This alpha value generally shows opacity of a pixel. For example, the alpha value is held in auxiliary data provided separately from color representation data for each pixel. The auxiliary data are generally called “alpha channel.”
FIG. 1 is a sequence diagram showing an example of print control processing where a PDL (i.e., Print Description Language) supports a bitmap with an alpha channel.
An application draws the bitmap with the alpha channel (which is a transmissive image), and outputs the transmissive image to an OS (i.e., Operating System) (S101). A printer driver receives the bitmap with the alpha channel (S102), and sends the bitmap with the alpha channel still attached (S103).
A printer performs a transparency process and printing based on the alpha channel because the printer driver supports the bitmap with the alpha channel.
On the other hand, sometimes the printer driver does not support the bitmap with the alpha channel. At this time, the printer driver sends the OS a notice being unable to process (i.e., not to support) the bitmap with the alpha channel. The OS outputs the drawing command in a format that does not need the alpha blending.
FIG. 2 is a sequence diagram showing an example of a print control process where a PDL that does not support a bitmap with an alpha channel is used.
Because a printer in this example does not support a bitmap with a alpha channel, the printer cannot receive the bitmap with the alpha channel from a printer driver. Therefore, the printer driver gives the OS a notice not to support the bitmap with the alpha channel.
An application draws a bitmap with a alpha channel (i.e., transmissive image), and outputs the transmissive image to the OS (S201).
The OS converts the transmissive image into a format that does not require the alpha blending, if the printer does not support the bitmap with the alpha channel (S202). The OS outputs a drawing command for the converted bitmap (which is a normal image) (S203). Here, in most cases, the drawing command output to the printer driver becomes a drawing command that uses a normal bitmap format.
The printer driver receives the drawing command that does not need the alpha blending, converts the drawing command into a PDL command, and sends the PDL command to the printer (S204).
Moreover, the printer that cannot perform the alpha blending process cannot implement a proper transparency process if the printer receives a drawing command of the bitmap with the alpha channel from the printer driver.
In contrast, Japanese Laid-open Patent Application Publication No. 2002-7102 (which is hereinafter called “Patent Document 1”) discloses an art that replaces an alpha blending specification by area information on the printer side depending on an alpha value, and converts a drawing command into a drawing command that performs processing depending on the area information.
However, in the conventional art, sometimes a bitmap, which is drawn by the printer, by the drawing command that does not need the alpha blending may differ from a bitmap displayed on an application screen.
In other words, in the conventional art, the transparency process is just performed improperly, and a transmissive image that the application expects cannot be drawn properly. For example, if the alpha value differs for each pixel, close alpha blending cannot be performed by the conventional art.